Volatile substance diffuser systems incorporating semipermeable membranes that permit the outlet of vapours but impede the escape of liquids are already known. These systems are based on a container, which consists of a heat-formed portion and a membrane. As the membrane is flat, the formed portion is designed with a flat circumferential lip where the heat-formed portion and the membrane are welded together. The heat-formed portion is designed so that it may contain the sufficient amount of liquid.
These systems are notable for being both economical and clean, as they prevent liquid being spilled in the event of improper handling.
No type of additional housing is included in their simplest applications, such as for instance in U.S. Pat. Nos. 4,157,787 and 5,518,790.
In other cases, this container is presented inside a usually plastic housing, which acts both as a protection and as a support. The housing also contributes to a better presentation of the product. As an example of systems with housings we may mention U.S. Pat. No. 4,849,606.
International patent application WO 2005/056063 A1 and European patent application EP 1319543 A1 describe one of these latter volatile substance diffuser systems. Thus, these documents describe a plastic housing which also has the function of regulating the system. For this purpose, the housing has an added element that is movable in relation to the housing, which performs the function of regulating the substance evaporated by means of partly or fully closing openings situated at the back of the housing.
These systems, however, have a series of drawbacks, which are explained below. On the one hand, the moving part which is added to the housing represents an extra cost, both in terms of a larger number of parts and of assembly. On the other hand, although the sealing of the openings is total, since there is a gap left between the membrane and the back of the housing, the device may go on evaporating, so that an inactive state of the system is never achieved.